Shorting switch



Feb. 21, 1956 'w. L. DAVIS 2,735,917

SHORTING SWITCH Filed June 29, 1953 3a lulll: 25 27 Ifnm. Z6

mg i United States Patent SHORTING SWHCH William L. Davis, Denver, Colo., assignor to Hathaway Instrument Company, Denver, Colo.

Application June 29, 1953, Serial No. 364,741

1 Claim. (Cl. 200158) The present invention relates to a shorting switch particularly suited for shorting low resistance shunt elements for a galvanometer.

Heretofore it has been common to provide shunt or multiplier devices for galvanometers which usually included a selector switch for connecting from 1 to 1000 ohm resistors in the circuit, a second selector switch for connecting from 1 to 10 100 ohm resistors in the circuit, and a series of resistors ranging from 40 ohms to 1 ohm to be shunted or shorted out of the circuit by means of two posts and a shorting length. These lengths were held in position by cap screws. It has been found that the necessity of moving the length into contact position and the requirement of loosening and tightening two screws is an inconvenience which frequently results in improper connection. Not infrequently one of the screws is improperly tightened so that the shorting action is incomplete. Of course this is particularly serious where it is desired to short out of the circuit resistors of A or 54 ohm. It, therefore, would be desirable to provide a shorting switch which would overcome the disadvantages heretofore encountered.

It, therefore, is an object of the present invention to provide a conveniently operable shorting switch for use in shunt o1- multiplier circuits for galvanometers.

It is a further object of the invention to provide a shorting switch having a single operating element which produces a wiping action and which is held under pressure to insure consistent low resistance contact.

A further object of the invention is to provide a switch for use on the panel of a shunt or multiplier resistor arrangement for galvanometers which will readily allow clear name-plate identification of the function of each switch.

Other and further objects of the invention subsequently will become apparent by reference to the following description taken in conjunction with the accompanying drawing wherein:

Figure 1 is an enlarged view of approximately twice actual size of the shorting switch comprising the present invention shown partially in cross-section; and

Figure 2 is an electric circuit diagram showing the connection of the switch into a typical shunt or multiplier circuit for a galvanometer.

Referring to Figure 1 it will be noted that the switch 24 comprises a metal member 25 having a knurled reduced diameter portion 26 which passes through a suitable opening in the panel 12. Adjacent to the knurled portion 26 is a threaded portion 27 engaged by a nut 28 which bears against the panel 12. The metal member 25 has an axial bore 29 which has an enlarged diameter portion fitted with an insulating sleeve 30. The lower portion of the member 25 has a reduced diameter portion 31 which is suitably knurled and fitted inside of a fiber insulating sleeve 32. The sleeve 32 engages a reduced diameter knurled portion 33 of a cooperating metal member 34 having an axially aligned threaded portion 35. It will be noted that adjacent surfaces of the conductive 2,735,917 ,Patented Feb. 21, 1956 members 25 and 34 are spaced apart by a space 36. A cap screw 37 having a head 38 extends through the axial bore of the member 25 within the insulating sleeve 29 so that it normally does not engage the member 25 unless the head 38 engages the panel end of the member 25. The member 25 is provided with a soldering lug 39, and similarly a soldering lug 41 is provided for the member 34. When it is desired to complete an electric circuit or short between the terminals 39 and 41, the cap screw 37 is moved to the position shown in Figure 2. The engagement of the cap screw head 38 on the surface of the member 25 produces a rubbing action to assure good electrical contact therewith. The action of the threads of the cap screw 37 on the threaded portion 35 of the member 34 assures good contact therewith since the bolt tends to compress the insulating cylinder 32. The insulating cylinder 32 is formed of suitable fiber insulation having a slightly resilient characteristic so as to maintain all contacts under consistent low resistance contact pressure when the screw 38 is moved to the position shown in Figure 1.

A typical electrical circuit for the apparatus is illustrated in Figure 2. It will be noted that the right hand binding post 13 is connected to the stud 15. When the link interconnects the studs 15 and 17, the link is actually placed in an inoperative condition. When the link is interconnecting the studs 15 and 18, a resistor 42 of suitable value is connected between the binding posts 13. When the link interconnects the studs 15 and 19, another resistor of a different value 43 interconnects the binding post 13. A conductor 44 extends from the left binding post 13 to a series of 1000 ohm resistors 45 connected between the eleven contacts of the switch 22. The switch arm of the switch 22 is connected by a conductor 46 to a series of ohm resistors interconnecting the eleven contact points of the switch 23. The switch 23 has a conductor 47 connected to a plurality of resistors having values of 40, 30, 20, 10, 4, 3, 2, 1, A and ,4 ohms respectively. These series resistors 48 are connected by a conductor 49 to the left binding post 14. The right binding post 14 is connected by a conductor 51 through the fuse 21 to the right binding post 13. It will become apparent that by the use of the switches 24 there may be inserted in series between the conductors 47 and 49 any resistance value from ohm up to 100 ohms, thus providing extremely fine determination of the total resistance to be effectively in series between the left binding posts 13 and 14. Thus this adjustment requires no links to be handled or changed, and the action of the screw head and threads assure a consistently low contact of proper pressure value.

While for the purpose of illustrating and describing the present invention certain preferred embodiments have been shown in the drawing, it is to be understood that the invention is not to be limited thereby since such other embodiments and variations are contemplated as may be commensurate with the spirit and scope of the invention set forth in the accompanying claim.

I claim as my invention:

A shorting switch for a low resistance galvanometer resistor comprising a cylindrical highly conductive metal member having a reduced diameter portion at each end, one portion being knurled so as to be mounted in a hole in an insulated panel, said reduced diameter portion terminating in a threaded portion adapted to receive a fastening nut, said member having an axial bore extending throughout its length, an insulating sleeve fitted within said bore, a second highly conductive cylindrical metal member, having a reduced diameter portion, reduced diameter portion of said latter member and the other reduced diameter portion of said first member being adjacent each other, and a second insulated sleeve surrounding said adjacent reduced diameter portions to support said second member in spaced relation and axial alignment with said first member, said second member having a threaded axial bore of smaller diameter than the bore of the sleeve in said first member, a cap screw engaging said threaded bore and extending through the sleeve of said bore of said first member, said cap screw having a head adapted to engage the reduced diameter end of said first member to complete an electric circuit between said two members and to tend to compress said 10 ,69 ,8 8

4 second insulating sleeve to insure a low resistance circuit connection at all times that the head of said screw engages the end of said first cylinder, and electric terminals connected to each of said cylindrical members for con- 5 nection to the terminal of a galvanometer resistor.

References Cited in the file of this patent UNITED STATES PATENTS White June 5, 1917 Lewis Dec. 21, 1954 

